1. Field of the Invention
The present invention relates to a method of repeated recording and quenching or erasing of deformation images on a surface of a recording material, which recording material is composed of a photoconductive, thermoplastic recording layer supported by an electrically non-conductive support layer and to an apparatus for carrying out the foregoing method.
2. Description of the Prior Art
Photothermoplastic recording materials having a photoconductive and thermoplastic recording layer as well as the various steps for the recording by electrostatic charging, informationwise exposure and thermal development to form a relief image are known, for example, from German Pat. No. 1,537,134. In general photothermoplastic recording materials consist of a support having a transparent and conductive layer, to which small quantities of a photoconductive layer are applied that consist of poly-N-vinyl carbazole and additives such as 2,4,7-trinitro fluorenone. A thermoplastic layer is applied thereon that consists, for example, of Staybelite-Ester 10.RTM., a hydrogenated colophony ester manufactured by Hercules. The coating technique and the sensitometric properties of such layers have been described in detail by, among others, Credelle et al., RCA Review, 33 (1972), pages 217 ff. The deformation images on such layers can after the recording be quenched by re-heating them until the relief image is smoothed, and the layer can then be imaged again. The relief images or deformation images are preferably holograms, which are recorded with the aid of laser beams.
Photothermoplastic layers containing poly-N-vinyl carbazole are also used in an embodiment in which the recording layer is applied directly to a flexible support layer, which may consist of polyester, for example, without a conductive intermediate layer (German Offenlegungsschrift No. 2,262,917). This recording material is of great interest in practice, because it works without the transparent and conductive layer, the application of which is technologically complicated. The recording and quenching or erasing of deformation images can be carried out in a manner similar to that including a recording material having a conductive intermediate layer. However, in the case of repeated recordings after previous quenching the image intensity becomes worse with each recording cycle, so that after less than 10 cycles it is impossible to make a recording and obtain a satisfactory image quality.
Compensating chargings. i.e. changing the charging polarity during a series of recordings, of photothermoplastic layers having pyrene resins as a photoconductor are known from German Offenlegungsschrift No. 2,233,878. Up to now this technique has not had any success with layers containing poly-N-vinyl carbazole. Such thermoplastic recording layers containing poly-N-vinyl carbazole were provided with a positive charge for the recording. In the case of a negative charge their light sensitivity was not sufficient for practical use.